1. Field of the Invention
The present invention relates to a charging method for a plurality of squibs which charge storage devices built or attached to the squibs which are connected to an ignition control device via a common bus, and can be selectively operated by electrical energy and an electrical signal which are supplied from the ignition control device.
Priority is claimed on Japanese Patent Application No. 2004-028090, filed Feb. 4, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
In an occupant restraint system used at the time of a collision as examplified by an air bag device, a gas is produced by combustion of the propellant mainly built in an occupant restraint system as high pressure gas which is used.
Moreover, an ignition element which plays a role in igniting the propellant is also built in the occupant restraint system with the propellant.
Each ignition element and an ignition control device which controls the ignition element is connected one-to-one via a harness.
However, there is a problem in that the number of ignition elements also increases by increasing the number of occupant restraint systems using the propellant mounted in a car, the number of harnesses increase in accordance with the increase of the number of the occupant restraint systems, and the need to remodel the ignition control device may arise.
On the other hand, there has been proposed a technology in which a plurality of squibs in which are built the ignition elements, ignition circuits which operate the ignition elements, and a communication circuit which is required in the case of communicating with the ignition control device are connected to a common bus extended from the ignition control device, and electric power is supplied from the ignition control device to all the squibs, while the ignition control device supplies the electrical signal only to a predetermined squib and ignites the ignition element (Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H10-154992; Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2000-241098).
Moreover, a squib which includes the communication circuit required in the case of communicating with the ignition control device via the bus, and the ignition circuit which operates the ignition element is proposed (Patent Document 2).
Furthermore, a technology which enables connecting the existing occupant restraint system with a bus without any changes by building an IC which holds the communication circuit, the ignition circuit, and the ignition element within a squib having a conventional external shape without modifying the existing occupant restraint system is being examined.
Furthermore, regarding the squib which builds or attaches the circuit for connecting the bus transmitting electric power and a data signal such as the squib attaching the communication circuit and the ignition circuit according to Patent Document 2, as an energy source which heats the ignition element and ignites the squib, a technique of accumulating electric power obtained from the ignition control device to the storage devices, such as condensers, via the bus is proposed.
In this way, in the state in which sufficient electric power is accumulated in the storage device, electric power which should be supplied from a bus to the storage device can be held down to a level required for supplementing the electric charge lost in natural electric discharge and the like.
However, when there are many squibs connected to the bus, the storage devices for supplying ignition energy which are built or attached the squibs also increase in proportional to the number of the squibs, but the amount of electric power from the bus is usually small.
For this reason, after the ignition control device begins to operate, it is necessary for a special charging technique to be used, and each storage device is charged to some degree in advance so that charging can be completed in a short time in preparation for a collision.
However, when the constitution in which, in the state of connecting a plurality of squibs to the bus, each storage device charges by drawing charging electrical current simultaneously from a bus is adapted, the failure of the bus itself or the ignition control device which supplies electrical current may arise when the input of electrical current is excessive.
Therefore, in order to prevent the above problem, a new electrical current restriction element or new electrical current restriction circuit should be introduced, and thereby the number of parts is increased, while the cost increases.
Moreover, when the constitution of performing the restriction of electrical current by resistance at the side of the ignition control device or each squib in order to suppress the total amount of input current at the time of starting charging is adopted, thereinafter, a large quantity (that is, a degree that a problem arises in the case of drawing electrical current to all squibs simultaneously) of electrical current cannot be drawn in each squib.
As a countermeasure therefor, a technique of performing restriction of electrical current with high resistance value only at the time of the initial charge has been considered. However, even if such a technique is used, when the total amount (the total capacity) of the storage devices increases or decreases, as the case may be, the ignition control device must change the amount of electrical current at the time of the initial charging.
In such a case, there is a problem in that an advantage of using the bus which does not need circuit change of the ignition control device is lost.
On the other hand, when the storage device acts as an ignition energy supply source in the squib, it is indispensable to diagnose the final initial charge and the fact of being a necessary and sufficient capacity by using a certain means.
In contrast, the adoption of a constitution of setting a diagnostic circuit in each storage device which is built in or attached to each squib connected to the bus has been considered.
However, it is important and necessary for the ignition control device to ultimately be able to comprehend a diagnostic result.
For this reason, when a complicated circuit or a complicated technique for each diagnosis itself is not required, the circuit and the communication protocol for transmitting the diagnostic result to the ignition control device by communication is required, and thereby there is a problem of increase in communication specifications or cost.